Mechanism

Transepidermal Water Loss

Water diffusing outward through the stratum corneum; rises when the barrier is disrupted.

Review

What it is

TEWL is the rate at which water moves from deeper skin out through the stratum corneum.

When barrier lipids and corneocyte structure are intact, TEWL stays low. Disruption — from disease, irritation, or harsh care — raises TEWL and dries the surface.

Why it matters

Elevated TEWL is a recurring marker in atopic dermatitis and many barrier-disrupted states.

Related mechanisms

StructureReview

Skin Barrier

Stratum corneum + lipid matrix that controls water loss and limits irritant entry.

PhysiologyReview

Hydration

Stratum corneum water content; central to texture, comfort, and barrier performance.

Ingredient axes

Ingredients that interact with this step

barrierReview

Moisturizer

Skin barrier axis

Formulations supporting the lipid barrier and reducing transepidermal water loss.

barrierClinical

Ceramides

Skin barrier axis

Lipids essential to stratum corneum structure; topical ceramides support barrier repair.

barrierReview

Occlusives

Skin barrier axis

Water-resistant agents (petrolatum, dimethicone, plant butters) that reduce TEWL.

barrierReview

Humectants

Hydration axis

Water-attracting agents (glycerin, hyaluronic acid, urea) that draw moisture into the stratum corneum.